Process and Device for Producing a Coated Structural Component

ABSTRACT

The present invention relates to a method of manufacturing a coated structural component ( 10 ) for a vehicle, comprising the steps of: providing a base component ( 11 ), hot forming the base component ( 11 ) into a molded component ( 12 ), electrochemically deburring the molded component ( 12 ), and electrolytically applying a corrosion protection layer ( 13 ) to the deburred molded component ( 12 ) to produce the structural component ( 10 ). The invention further relates to an apparatus for carrying out a method according to the invention for producing a deburred and coated structural component.

The present invention relates to a method of manufacturing a coated structural component for a vehicle. The invention further relates to an apparatus, in particular an industrial plant, for producing such a structural component.

In the automotive industry, hot formed components are used for the production of body-in-white. Various process variants are known for the production of formed components. On the one hand, uncoated sheet metal components are used which are hot formed and hardened in a so-called direct process from a flat uncoated sheet metal. According to another variant, sheet metal components are coated with an alloy, for example an aluminum-silicon alloy, in a steel mill and then also hot-formed and hardened in a direct process. This variant is by far the most commonly used in practice. As an alternative to this process, coated, for example galvanized sheet metal, components are used, which are cold formed and trimmed to the desired dimensions. Only then is the component heated and hardened in a tool. This process is called the indirect process.

In practice, direct process methods are preferred because they are generally faster and easier to carry out, and are more cost-effective due to lower tool investments. As an alternative to the processes described above, a process was developed in which the sheet metal components to be produced are first hot formed in the direct process and then electrolytically coated with a corrosion protection layer. In order to drive out any hydrogen from the material, the components are then annealed. The problem, however, is that an oxide layer of the sheet metal components, which is formed when heated to 900° C. for example, regularly flakes off during the forming process. This means that the formation of oxides on the circuit board before it is inserted into the tool cannot usually be completely avoided. The build-up of oxides in the tool leads to grooves in the component as well as to the throw-up of material in the edge region of the grooves. The throw-up can be sharp-edged and/or form peaks. If the peaks and/or throw-ups are too high, they can no longer be adequately covered by a subsequent and/or additional coating. In the event of subsequent stress during the use phase of the vehicle due to moisture and/or salt for example, there is a risk that the structural component will begin to corrode starting from these peaks. The peaks should therefore be prevented or at least reduced as far as possible.

It is an object of the present invention to at least partially address the foregoing problem. In particular, it is an object of the present invention to provide a method and an apparatus for producing a coated structural component made from a sheet metal component while avoiding or reducing peaks and/or throw-ups.

The preceding task is solved by the patent claims. In particular, the foregoing problem is solved by the method as described and claimed herein and the device as described and claimed herein. Further advantages of the invention result from the subclaims, the description and the figures. In this context, features described in connection with the method naturally also apply in connection with the apparatus according to the invention and vice versa in each case, so that reference is and/or can always be made mutually with regard to the disclosure concerning the individual aspects of the invention.

In accordance with a first aspect of the present invention, a method of manufacturing a coated structural component for a vehicle is provided. The method comprises the following steps/stages:

-   -   providing a base component,     -   hot forming of the base component into a molded component,     -   electrochemical deburring of the molded component, and     -   electrolytic application of a corrosion protection layer to the         deburred molded component.

In the context of the present invention, it has been recognized that the process of electrochemical deburring may advantageously be implemented in a direct process for manufacturing a structural component for a vehicle. That is, the method is particularly to be understood as a method for manufacturing a coated structural component for a vehicle according to a direct process. Compared to conventional forming processes, structural components with an improved surface quality, in particular without peaks and/or throw-ups which can subsequently lead to damages to the structural component, can thus be created in a simple and reliable manner. A correspondingly advantageous corrosion resistance can be achieved by a corrosion protection layer covering the entire surface. Due to the electrochemical deburring, a relatively thin corrosion protection layer is already sufficient to achieve the desired surface coverage.

A further advantage in the procedure according to the invention is that no special precautions need to be taken with respect to the base component during hot forming. That is, no special temperature and/or heating curves need to be observed and/or restrictions in this respect need to be taken into account. The heating process can thus be carried out in a accordingly simple manner. In particular, an uncoated base component, preferably in the form of a sheet metal component, is used for the base component. For example, a simple sheet metal component, in particular a simple sheet steel component, such as a sheet metal component made of 22MnB5 steel or of manganese-boron steel having a tensile strength of about 2000 MPa, may be used. The sheet metal component may be understood as a circuit board. The base component may have a thickness in a range between 0.5 mm and 6 mm, in particular in a range between 0.7 mm and 3 mm. The base component may have different sheet thicknesses at different locations and/or different materials at different locations within the specified range. Furthermore, the base component may have different strengths at different locations, which may be achieved, for example, by different cooling curves.

The electrochemical deburring and the electrolytic application of the corrosion protection layer are preferably carried out directly one after the other. That is, right after the molded component has been electrochemically deburred, it can be directly moved for the electrolytic application of the corrosion protection layer, for example into an immersion bath and/or at least partially into a suitable electrolyte.

Hot forming is preferably performed in a direct process. In the hot forming process, the base component is first heated to a pre-definable temperature, for example to a temperature in a range between 800° C. and 1000° C., and then formed or shaped into the desired shape. When heating the base component, scaling of the base component can be reduced by using an inert gas in the furnace or by using a vacuum furnace.

The structural component can be understood in particular as a body component for a vehicle. Within the scope of the process, several structural components can also be produced simultaneously. In particular, several molded components can be electro-chemically deburred at the same time.

For electrochemical deburring of the molded component, the molded component to be deburred is preferably suspended in a rack. The cathode or a plurality of cathode parts can be selectively positioned in the rack for smoothing or deburring the desired area on the molded component. The cathode or cathode portions may follow the geometry of the molded component. Preferably, the cathode comprises an electrically conductive material, in particular stainless steel or titanium. The cathode is preferably provided as a flat or wire-shaped component. In the process of deburring, the molded component forms the anode. The electrochemical deburring is preferably performed selectively on area sections of the molded component, that is in particular not or at least not selectively on end edges, end portions and/or projections of the molded component.

According to a further embodiment of the present invention, it is possible that in a process the molded component has at least one forming edge with a forming radius produced by the hot forming, wherein the electrochemical deburring is carried out for deburring at least one area section adjacent to the at least one forming edge, that is, for selectively removing, for example, grooves in the area sections adjacent to the at least one forming edge. In other words, the electrochemical deburring is selectively carried out on area sections of the molded component which are configured adjacent to the at least one forming edge, and in particular not, or at least not selectively, on the at least one forming edge, end edges and/or end portions of the molded component. Accordingly, also the electrolyte, the temperature of the electrolyte, the treatment time for the deburring and in particular the positioning of the at least one cathode on the molded component are designed or determined with reference to the at least one area section to be deburred. In the prior art, it is generally known to electrolytically deburr complex components and/or in particular their cut and/or manufacturing edges or end edges. According to the invention, however, electrochemical deburring is now used specifically for deburring segments and/or surfaces of the component which are subjected to relative movement between the workpiece and the tool during forming and are thus subject to the potential risk of grooving. According to the invention, this can be easily and effectively integrated into the previously known manufacturing process comprising electrochemical coating of a molded component. In the process, at least two forming edges can be produced by the hot forming, wherein the electrochemical deburring is carried out for deburring at least one area section between the at least two forming edges. In this context, the area section may be understood in particular as a straight and/or planar area section or, apart from any grooves, a straight, planar and/or relatively smooth area section. The forming radius may be understood as a bending radius, an inner radius and/or an outer radius of the at least one forming edge and/or at the at least one forming edge.

In a process according to the invention, in particular a zinc coating is applied as a corrosion protection layer. The zinc coating may be understood as a zinc-containing coating and/or alloy. The application of a corrosion protection layer can thus be understood as galvanizing. Preferably, the zinc coating is applied as part of an electrolytic coating process. For electrolytic coating of the component, the latter may remain in the rack described above. In this case, the molded component with the rack is immersed in a suitable electrolyte and is connected as the cathode. The purest possible zinc is used for the anode. Additional anodes can be positioned close to the component to specifically influence the zinc layer. In the context of the invention, it is proposed, as it were, to electrochemically deburr the molded component in the process sequence of galvanizing prior to galvanizing. In this way, as already mentioned-above, build-up at the edge of the grooves as well as, at least in part, the grooves of the at least one molded component or in the region of an oxide layer of the molded component can be reduced to the desired minimum. Molded components have so far been produced either uncoated, i.e. without corrosion protection, without cathodic corrosion protection, or with, for example, a zinc-iron coating, in which cathodic corrosion protection is provided but there is an electrochemical potential to galvanized components, for the reasons stated in the introduction to the description. By the intermediate step of electrochemical deburring proposed in accordance with the invention and the subsequent electrolytic galvanizing, the desired corrosion resistance can now be achieved in a simple and reliable manner and without any loss of quality. In electrochemical deburring, the molded component represents the anode and is at least partially immersed in an electrically conductive liquid, i.e. an electrolyte, during the process. The temperature of the electrolyte may be or may be set in a range between 30° C. and 50° C. during the deburring process. The cathode and/or cathode elements may be adapted to the geometry of the component for this purpose. Compared to conventional galvanizing processes of uncoated and preformed sheet metal components, significantly smoother surfaces can be coated evenly and closed with a relatively thin zinc layer.

According to a further embodiment of the present invention, it is possible that in a process a cathodic dip coating is applied to the coated molded component after the application of the zinc coating. It has been shown that a cathodic dip coating applied in addition to, for example, a zinc coating does regularly not sufficiently cover the surface of the structural component due to burrs in the molded component or in the originally formed base component. Thus, in particular, edges and/or tips which may still be pronounced in the first corrosion coating can no longer be sufficiently covered by the relatively thin cathodic dip coating. In other words, the tips of the grooves and/or ejections, which are usually still covered with zinc, are only insufficiently covered or not covered at all by the subsequent cathodic dip coating. These spots can relatively quickly be the starting point of corrosion. By deburring according to the invention before the first coating process, this problem can be satisfactorily taken into account.

When carrying out the process according to the invention, it has been shown that a layer thickness of the cathodic dip coating in a range between 10 μm and 40 μm can already be sufficient to provide a cathodic dip coating covering the entire surface. In other words, the cathodic dip coating can be applied with a layer thickness in a range between 10 μm and 40 μm, in particular in a range between 15 μm and 25 μm.

Using a method according to the present invention, it is further possible that the electrochemical deburring of the molded component is carried out by means of a cathode and an anode, wherein the molded component is used as at least a part of the anode and the cathode for the electrochemical deburring is positioned at a distance of less than 30 mm from at least one forming edge and/or a surface of the molded component to be deburred at the forming edge. In particular, the cathode may be positioned at a distance in a range between 5 mm and 30 mm, in particular between 10 mm and 20 mm, from the at least one forming edge and/or surface. In experiments within the scope of the present invention, this distance has been found to be particularly advantageous for achieving the desired deburring reliably and yet with a relatively low effort for producing a tool for suitable positioning of the formed component. Selectively positioning the cathode in proximity to the at least one forming edge provides effective deburring. The cathode may comprise a plurality of cathode elements. The cathode may be configured and/or fixed in a tool, for example in the form of a rack, in which the molded component is at least partially positioned in an electrolyte in a predefined position for electrochemical deburring.

Furthermore, in a process according to the invention, the electrochemical deburring can be performed with an electrolytic current density in a range between 5 A/dm² and 15 A/dm². An operating time or time duration for the electrochemical deburring is preferably set to a value between 3 minutes and 12 minutes, in particular between 5 minutes and 10 minutes. In other words, the electrochemical deburring may be carried out for a corresponding period of time. For this purpose, the electrodes used, the currents used and/or the electrolyte may be adjusted and/or positioned accordingly. With the above-described operating time and/or current density, advantageous deburring can be performed. Furthermore, it has been found advantageous if an electrolyte comprising sodium sulfate and sodium chloride is used in a method according to the present invention for electrochemical deburring, wherein at least twice as much sodium sulfate is used as sodium chloride. An electrolyte containing three times as much sodium sulfate as sodium chloride, for example in a ratio of 180g/I sodium sulfate to 50g/I sodium chloride, has been found to be particularly advantageous.

According to another aspect of the present invention, an apparatus for carrying out a method, as described in detail above, for producing a deburred and coated structural component in the form of a body component for a vehicle is provided. For carrying out the method, the apparatus, in particular in the form of an industrial plant, may comprise a provisioning tool for providing the basic structural component. The apparatus further comprises a forming tool for forming the base component into the formed component, a deburring tool for performing the electrochemical deburring and/or a coating tool for performing the electrolytic application of the corrosion protection layer and/or the cathodic dip coating. Thus, the apparatus according to the invention brings the same advantages as have been described in detail with reference to the process according to the invention.

Further measures improving the invention will be apparent from the following description of various embodiments of the invention, which are shown schematically in the figures. All features and/or advantages, including constructional details and spatial arrangements, arising from the claims, the description or the figures may be essential to the invention both individually and in the various combinations.

It is schematically shown in each case:

FIG. 1 a flow chart explaining a process according to one embodiment of the present invention,

FIG. 2 a flow chart explaining further details of the process according to the invention,

FIG. 3 a flow chart explaining an exemplary procedure for manufacturing a structural component according to the invention, and

FIG. 4 a formed structural component known in the prior art.

Elements with the same function and mode of operation are each given the same reference signs in the figures.

FIG. 1 shows the various process steps for manufacturing a structural component 10 for a motor vehicle according to a preferred embodiment. As shown in FIG. 1 , base components 11 having a thickness of about 1.4 mm are first cut from a coil 18. The sheet metal components are then heated to about 900° C. in a furnace 22, and then formed into the desired shape by a forming tool 20. That is, the heated and uncoated base components 11 in the form of blanks are formed into molded components 12 by the forming tool 20. Even before the molded components are now coated, they are trimmed and then electrochemically deburred. For this purpose, the molded component 12, which forms an anode 17 via the rack for suspending the molded component 12 in the electrolyte, is positioned on a cathode 16 or on plate-shaped cathode components. More specifically, the cathode 16 or plate-shaped cathode components are positioned at a distance of about 10 mm from the molded component 12, respectively, at an area section 14 between two forming edges 15 on the surfaces to be deburred.

Electrochemical deburring is carried out with an electrolytic current density of approx. 10 A/dm² for approx. 8 minutes. The electrolyte used is a liquid containing about 180g/I sodium sulfate and 50g/I sodium chloride at a temperature of about 40° C. Next, the electrochemically deburred molded component 12 is coated with a corrosion protection layer 13 shown in FIG. 2 to produce the structural component 10. More specifically, a zinc coating is applied to the deburred molded component 12 by moving the deburred molded component 12 through an electrolyte 19. After the application of the corrosion protection layer 13, a cathodic dip coating 21 shown in FIG. 2 is also applied to the coated molded component 12 with a coating thickness of about 20 μm over the entire surface. For this purpose, the molded component 12 or structural component 10 coated with the corrosion protection layer 13 is moved through a cathodic dip coating bath 23.

The tools and aids for carrying out the process shown in FIG. 1 may be understood as components of an apparatus for carrying out the process and thus for producing the deburred and coated structural component 10.

FIG. 2 shows the deburring and coating process in further detail. As can be seen in FIG. 2 , after forming, the molded component 12 has edges and peaks that protrude more than average in the area of an area section 14 upon closer inspection. These are removed or reduced and/or smoothed by the electrochemical deburring process. Thereupon, the corrosion protection layer 13 is applied in the form of the zinc coating. Subsequently, the cathodic dip coating 21 is applied.

With reference to FIG. 3 , further embodiments for manufacturing the structural component 10 are described. In a first step 51, the coil 18 is provided, from which, in a second step S2, the base component 11 is then provided in the form of a circuit board. In a direct process, the base component 11 is now heated to about 900° C. in step S3, and formed and press-hardened in step S4. In an indirect process, the base component 11 is first cold formed in step S2 a, which is performed after step S2, and then trimmed to the desired shape in step S2 b. In the indirect process, heating according to step S3 follows only thereafter. Step S2b can initially be omitted in the indirect process. In the direct process, press hardening or hot forming is usually carried out by means of intermediate cooling. In the direct process, step S3 is followed by trimming the molded component 12 in step S4 and cleaning the molded component 12 in step S5. In step S6, the molded component 12 is now cleaned and, in this process, electrochemically deburred as described in detail above. In the indirect process, steps S4 and S5 may be skipped. In step S7, galvanizing follows. The molded component 12 can already be considered as the structural component 10 described above. Step S7 is followed by annealing in step S8. The cleaned, galvanized and annealed structural component 10 is now oiled in step S9 to produce a transport protection. In the subsequent step S10, an assembly of possible sub-components of the structural component 10 may take place. In step S11, a further cleaning process takes place. Subsequently, the structural component 10 is coated with a cathodic dip coating 21 in step S12, which up to this point may also in principle still be regarded as a molded component 12.

FIG. 4 shows a prior art structural component 10 a in which the molded component 12 has not been deburred prior to galvanizing. In this case, the edges and tips are still covered by the first corrosion protection layer 13. However, the cathodic dip coating 21 is penetrated by the anti-corrosion layer 13, as a result of which the structural component 10 a has only a correspondingly lower corrosion resistance.

The invention admits of further design principles in addition to the embodiments illustrated. That is, the invention is not to be considered limited to the embodiments explained with reference to the figures.

LIST OF REFERENCE SIGNS

10 Structural component

10 a Structural component

11 Base component

12 Molded component

13 Corrosion protection layer/ zinc coating

14 Area section

15 Forming edge

16 Cathode

17 Anode

18 Coil

19 Electrolyte/ Zinc bath

20 Forming tool

21 Cathodic dip coating

22 Furnace

23 Cathodic dip coating bath 

1. A method of manufacturing a coated structural component for a vehicle, comprising: providing a base component, hot forming of the base component into a molded component, electrochemical deburring of the molded component, and electrolytic application of a corrosion protection layer to the deburred molded component to produce the structural component.
 2. The method according to claim 1, wherein the molded component has at least one forming edge produced by the hot forming and having a forming radius, wherein the electrochemical deburring for deburring at least one area section is carried out adjacent to the at least one forming edge.
 3. The method according to claim 1, wherein a zinc coating is applied as corrosion protection layer.
 4. The method according to claim 3, wherein after the zinc coating has been applied, a cathodic dip coating is applied to the coated molded component.
 5. The method according to claim 1, wherein the cathodic dip coating is applied with a layer thickness in a range between 10 μm and 40 μm.
 6. The method according to claim 2, wherein the electrochemical deburring of the molded component is performed by means of a cathode and an anode, the molded component being used as at least part of the anode and the cathode for the electrochemical deburring being positioned at a distance of less than 30 mm from the at least one forming edge.
 7. The method according to claim 1, wherein the electrochemical deburring is performed with an electrolytic current density in a range between 5 A/dm² and 15 A/dm².
 8. The method according to claim 1, wherein the electrochemical deburring is performed over a period of time in a range between 3 minutes and 12 minutes.
 9. The method according to claim 1, wherein an electrolyte comprising sodium sulfate and sodium chloride is used for electrochemical deburring, wherein at least twice as much sodium sulfate as sodium chloride is used.
 10. An apparatus for carrying out a method according to claim 1 for producing a deburred and coated structural component in the form of a body component for a vehicle. 